Eurycoma longifolia is used for reducing cortisol levels and raising testosterone levels in persons under stress. A method for promoting weight reduction includes administering to a human having a caloric deficit an effective dose of Eurycoma longifolia for reducing cortisol levels and raising testosterone levels relative to respective cortisol and testosterone levels that would result in the absence of the administration of the Eurycoma longifolia. A method for promoting improved endurance aerobic performance in a human includes administering, within thirty minutes before aerobic exercise or during the aerobic exercise, to a human subject an effective dose of Eurycoma longifolia for reducing cortisol levels and raising testosterone levels in the human subject relative to respective cortisol and testosterone levels that would result in the absence of the administration of the Eurycoma longifolia.